A Light-Emitting Diode (LED), as used herein, is a semiconductor light source for generating light at a specified wavelength or a range of wavelengths. LEDs are traditionally used for indicator lamps, and are increasingly used for displays. An LED emits light when a voltage is applied across a p-n junction formed by oppositely doping semiconductor compound layers. Different wavelengths of light can be generated using different materials by varying the bandgaps of the semiconductor layers and by fabricating an active layer within the p-n junction.
A phosphor material is usually added to change the properties of light generated by the LED. For example, monochromatic light provided by an LED can be converted to polychromatic light through the application of several phosphors, either in a mixture or several phosphor layers. The phosphors Stokes shift a shorter wavelength light to a longer wavelength. The perception of white light may be evoked by generating mixtures of wavelengths that stimulate all three types of color sensitive cone cells (red, green, and blue) in the human eye in nearly equal amounts and with high brightness compared to the surroundings in a process called additive mixing. A white light LED may be used as lighting, such as back lighting for various display devices, commonly in conjunction with a liquid crystal display (LCD).
LEDs are made by growing a plurality of light-emitting structures on a substrate. When separated, the light-emitting structures are referred to as LED dies. Electrodes or conductive pads, reflectors, lenses, packaging substrate, and optionally one or more phosphor materials are combined with the plurality of light-emitting structure to create optical emitters. The phosphor material is typically dispensed on a LED die that is attached to a package substrate. In some cases, the phosphor material is coated on the LED die in a uniform thickness coating.
While existing methods of packaging an LED have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. More efficient methods and designs that extract more of the light generated and improve light and color distribution continue to be sought.